The long-term goals are to understand the mechanism of cellular hypersensitivity or immunity in man and determine the cause of defects in this immune function in certain human diseases which are associated with depressed immunity. A better understanding of the defects should lead to improved methods of therapy for such patients in particular and in certain infectious diseases in general. Cellular immunity is considered important in other biologic phenomena especially transplantation and tumor immunity. Such information should be of use in these areas as well. Specifically, it is proposed to investigate: 1) The observation that lymphocyte proliferation can be dissociated from mediator production. Heterogeneity in lymphocyte function will be clarified to determine whether specific subpopulations of lymphocytes exist, some proliferating in response to antigens, others making mediators. It is also of interest to determine whether different lymphocytes make different mediators. 2) Development of methods to study human monocyte function in vitro relating to their response to lymphocyte mediators and to assay monocyte function in patients with depressed delayed hypersensitivity. 3) Evaluate the effect of dialyzable transfer factor on the clinical course of patients with depressed cellular hypersensitivity and chronic infection.